Multialkali phosphate glasses: a new window to understand the mechanism of ion transport

Abstract

Alkali metaphosphate glasses containing two and three alkalis have been prepared by melt-quenching method over a wide range of compositions. Several properties of these glasses such as density, molar volume, glass transition temperature, heat capacity jump and NMR chemical shift of ³¹P, ²³Na and ⁷Li nuclei have been measured. Transport properties have been studied over a wide range of frequency and temperature. Mixed alkali effect (MAE), which manifests in three alkali containing glasses is found to be complex. Arrhenius plots of d.c. conductivities are characterized by two slopes and a.c. conductivities display two power-law regimes with two characteristic s values. The imaginary part of the electric modulus exhibits a unique two peak relaxation behaviour and the peaks merge at higher temperatures. This is first time such a behaviour has been observed in a.c. conductivity and dielectric relaxation of glasses. A new mechanism has been proposed to understand ion transport in oxide glasses, which rationalizes all the observations made in the trialkali phosphate system examined here.